The man in custody for allegedly killing 12 people at the screening of the latest Batman movie in Aurora, Colorado told authorities after the shooting that he "was The Joker," NYPD police commissioner Ray Kelly said today.

Kelly told reporters the suspect, identified by federal officials as 24-year-old James Holmes, had dyed his hair like The Joker. The Joker is a well-known villain in the fictional Batman universe. The attack took place at a screening of "The Dark Knight Rises," the final movie in a Batman trilogy, following "The Dark Knight" in which The Joker was the principal villain.

Two federal law enforcement officials confirmed the details of The Joker reference to ABC News. Aurora police chief Dan Oates declined to comment on Kelly's remarks but said he had spoken with the NYPD, where he had previously served.

Police said the weapons used in the massacre include a military-style AR-15 assault rifle with a high-capacity drum-style clip, a shotgun and two handguns. The guns were purchased legally over the last several months, according to law enforcement officials.

Holmes does not have a criminal record except for a traffic violation, which would allow him to pass any background check for weapons, law enforcement sources said. A local pawn shop owner said that Holmes never bought any firearms there but believed he had been in the shop before talking about guns.

"Since I do see a lot of people in and out of my shop, I don't remember all conversations that I have with everybody," Hillcrest Pawnbrokers owner David Casper told ABC News. "But when they started mentioning the firearms that he had, it sounded very much like the firearms I recommend to my customers... I immediately put that connection together."

Police also said they believe Holmes' apartment, just five miles from the theater, is rigged with explosive booby-traps and are cautiously exploring the residence with remote-controlled cameras. Authorities told ABC News the place appeared to wired to explode if police had raced through the doors -- a plan to add even more to the night's body count.

"It's another tragic event from an obviously deranged individual," Aurora City Councilman Bob LeGare told ABC News. "I don't know what more can be said."

Witnesses Describe Deadly Rampage

Witnesses to the shooting said that a man appeared at the front of the theater about 20 minutes into the movie with a rifle, handgun and gas mask. He then threw a canister that released some kind of gas, after which a hissing sound ensued, and he then opened fire on the crowd packed into the early-morning screening of the film. Wintesses said that during the shooting the man appeared to be dressed in all black and police later said he was wearing several pieces bullet-proof armor and a gas mask.

"We were maybe 20 or 30 minutes into the movie and all you hear, first you smell smoke, everybody thought it was fireworks or something like that, and then you just see people dropping and the gunshots are constant," witness Christ Jones told ABC's Denver affiliate KMGH. "I heard at least 20 to 30 rounds within that minute or two."

A man who talked to a couple who was inside the theater told ABC News, "They got up and they started to run through the emergency exit, and that when she turned around, she said all she saw was the guy slowly making his way up the stairs and just firing at people, just picking random people."

"The gunshot continued to go on and on and then after we didn't hear anything," the couple told the man. "We finally got up and there was people bleeding, there was people obviously may have been actually dead or anything, and we just ran up out of there, there was chaos everywhere."

Radio communication between police and emergency responders released by authorities describe a desperate situation for those first on the scene.

"Get us some damn gas masks. We can't get in," one officer says after confronting the heavy smoke in the theater.

"I've got a child victim," said another who was waiting outside for help.

After waiting on ambulances for a few minutes, police began taking victims to the hospital in their own patrol cars.

"I've got a whole bunch of people shot in here and no rescue," one of the officers said.

When it was over, 12 people were dead and another 59 were wounded.

Acquaintance: Holmes Unalarming, 'Kind of Geeky'

Jackie Mitchell, who lives a block from Holmes' apartment in Aurora, said he had several beers with Holmes just days before the shooting and Holmes did not show any angry or anti-social tendencies.

"He seemed kind of geeky," Mitchell said. "We just talked about football… that kind of thing."

When he saw today's news reports, Mitchell said, "I don't have any hair and my hair stood up when I saw the dude's picture."

The FBI said approximately 100 of its agents are on the scene assisting with the ongoing investigation.